Micro CT is widely used in many applications, for example, for hidden defect inspection in semiconductor, electronics, advanced material and bioscience industries. One increasingly important category of the applications is the internal layer separation and inspection of planar multi-layered electronics as advanced packaging technologies are becoming dominant in the manufacturing process. To obtain the pattern of each individual layer and to check the quality of the corresponding manufacturing process, it is a general requirement from users to non-destructively separate the individual layers parallel to the primary plane of the object.
There are several current common approaches. FIG. 1A illustrates a general reconstructed CT image or reconstruction matrix 30. A first approach typically taken is shown in FIG. 1B to reconstruct one slice first, with which one manually measures the slant angle 36 of the reconstructed image 30, and restarts the reconstruction process for all slices with that angle identified 36 of the reconstructed object 30. The slant angle 36 of the object 30 is measured in a conventional system by picking two points along the edge 34 and applying a triangular function. Then the measured angle is used in a re-reconstruction process as the starting angle which leads to the edges of the reconstructed image aligned with the dimensions of the reference plane and reconstruction matrix to render the orientated reconstructed image ore reconstructed slices of a multi layered planar object 32 shown in FIG. 1E.
In another approach the slant angle 46 of the reconstructed image 30 is also calculated, as shown in FIG. 1C, however, instead of re-reconstructing the CT slices as shown in the system shown in FIG. 1B, an image rotation 44 is performed of the angle identified 46 relative to a reference plane/reconstruction matrix dimension 48 of all the reconstructed images 32 to achieve the preferred orientated reconstructed image 42 shown in FIG. 1E.
In another approach, shown in FIG. 1D, the primary plane of the reconstructed object is carefully identified and then defined as the clipping plane so that the internal layers can be displayed properly. The object projection is cut along the direction defined by the cut-plane (or clip-plane) 54. The cut-plane is defined carefully to match with a cut-plane angle 56(α) as accurate as possible the orientation of the object which is generally a time-consuming process requiring skilled operators. The cut plane angle is defined as the angle formed between the normal of the cutting plane 55 and the normal of the reference plane or reconstruction matrix dimension 49.
All the above mentioned conventional methods need to manually determine the object orientation after the reconstruction for at least one slice and then perform image rotations or redo the reconstruction. This not only slows down the image processing and adds additional computing resource, but also makes the layer separation and interpretation work only accessible to well-trained users.
There is a need for CT reconstruction method for planar objects with automatically determined orientation that addresses at least one of the above limitations in the prior art.